Q.74 Choose the correct answer from the Match List I with List II :
List I – DNA Replication Protein
- (A) DNA Polymerase III
- (B) DNA Polymerase I
- (C) DNA ligase
- (D) Tus
List II – Function
- (I) Binds to ter sequences and prevents the advancement of the replication fork
- (II) Synthesizes DNA in the leading and lagging strands
- (III) Removes RNA primers, fills in gaps with DNA
- (IV) Covalently attaches adjacent Okazaki fragments
Choose the correct answer from the options given below :
- (1) (A)-(II), (B)-(IV), (C)-(I), (D)-(III)
- (2) (A)-(II), (B)-(IV), (C)-(III), (D)-(I)
- (3) (A)-(II), (B)-(III), (C)-(IV), (D)-(I)
- (4) (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
DNA replication proteins like DNA Polymerase III, I, ligase, and Tus each have specific roles in bacterial replication, from synthesis to termination. The correct matching pairs them accurately with their functions.
Protein Functions
These enzymes coordinate E. coli DNA replication, ensuring accurate duplication of the genome.
-
DNA Polymerase III (A): Main replicative enzyme; synthesizes leading and lagging strands (II).
-
DNA Polymerase I (B): Removes RNA primers, fills gaps with DNA (III).
-
DNA ligase (C): Seals nicks between Okazaki fragments (IV).
-
Tus (D): Binds Ter sites, blocks replication fork progression (I).
Option Analysis
| Option |
Matching |
Issues |
| (1) |
A-II, B-IV, C-I, D-III |
Ligase not fork blocker; Pol I not ligase . |
| (2) |
A-II, B-IV, C-III, D-I |
Pol I not ligase; ligase not primer removal . |
| (3) |
A-II, B-III, C-IV, D-I |
Correct; all align precisely . |
| (4) |
A-IV, B-III, C-I, D-II |
Pol III not ligase; Tus not synthesis . |
Correct answer: (3).
DNA replication proteins matching questions assess core bacterial mechanisms: DNA Polymerase III for bulk synthesis, Pol I for primer processing, ligase for fragment joining, Tus for termination at Ter sites—key for molecular biology exams like GATE Life Sciences.
Replication Process Overview
Replication forks progress bidirectionally; Pol III extends primers on both strands, Pol I matures fragments, ligase seals, Tus halts forks circularly.
Correct Matches Table
| Protein (List I) |
Function (List II) |
Role Detail |
| (A) DNA Pol III |
(II) Leading/lagging synthesis |
Processive holoenzyme |
| (B) DNA Pol I |
(III) Primer removal/gap fill |
5′-3′ exo/polymerase |
| (C) DNA ligase |
(IV) Okazaki sealing |
ATP-dependent nick repair |
| (D) Tus |
(I) Ter binding/fork stop |
Bidirectional termination |
Why Other Options Fail
Options 1/2 swap ligase/Pol I roles; 4 misassigns synthesis/termination. Memorize: Pol III (main), Pol I (maturation), ligase (join), Tus (stop) for quick recall.
